onresize to control the time after which the event fires. observe() to make it look for changes to a specific element's size. Get tips on how to implement it in your own web application and see the benefits of using it. Uses ResizeObserver to do the work. The "for (let entry of entries)" loop enumerates all entries but I need only the id of the element that has been resized. createElement ('div'); wrapper_2. Jan 4, 2018 · I'm a bit surprised that in order to listen to changes on elements dimensions (not window Object) we have to use a new interface called ResizeObserver. The oven (your webpage) needs to monitor the cake (an element) as it expands. Unlike window resize events, which only detect modifications to the viewport, ResizeObserver can be attached to any element and will notify you when that element's dimensions change. Oct 11, 2024 · The ResizeObserver interface monitors changes in the dimensions of an element and delivers notifications to the observer whenever those changes occur. If the resize event is triggered too many times for your application, see Optimizing window. Saves 3 hours of debugging. querySelectorAll (selectors); // create the div to wrap your elements const wrapper_2 = document. A minimal library which polyfills the ResizeObserver API and is entirely based on the latest Draft Specification. resize — embrace the native solution built for modern web layouts. unobserve (elementToObserve); Alternatively, to stop observing all elements currently being monitored by a ResizeObserver instance, you can use the disconnect() method: resizeObserver. Dec 28, 2021 · This web development tutorial will cover how to import and work with the ResizeObserver within your Angular applications. It reacts to changes in size of any of the observed elements, independent of what caused the change. disconnect() to stop tracking the element when the component is unmounted. A fundamental … Jan 14, 2020 · Considering the ResizeObserver constructor, whose first argument is a callback which accepts two arguments, first of which is an array of ResizeObserverEntry objects, what are the differences between Jan 31, 2022 · Detecting element size changes is something that is normally difficult to do, but with resize observer it is incredibly easy. Watching multiple elements import { ResizeObserver } from '@juggle/resize-observer'; const ro = new ResizeObserver((entries, observer) => { console. 1. Jun 23, 2025 · The observe() method of the ResizeObserver interface starts observing the specified Element or SVGElement. Nov 7, 2025 · The ResizeObserver interface reports changes to the dimensions of an Element's content or border box, or the bounding box of an SVGElement. Nov 7, 2025 · The Resize Observer API provides a performant mechanism by which code can monitor an element for changes to its size, with notifications being delivered to the observer each time the size changes. querySelectorAll () results in an error. Resize Observer API 提供了一种高性能的机制，通过该机制，代码可以监视元素的大小更改，并且每次大小更改时都会向观察者传递通知。 Dec 30, 2023 · The basic usage of ResizeObserver involves creating an instance of the observer, specifying the target element (s) to observe, and defining a callback function that will be triggered when a size Oct 14, 2019 · The Hook I created the useResponsiveBreakpoints hook which accepts the ref of the element we want to observe size changes on and a list of named breakpoints. . Latest version: 9. Disconnect the Observer (When Necessary): When you no longer need to monitor an element, use the unobserve() method. Is there any performance implications of doing this vs instantiating multiple ResizeObserver s for observing different elements or groups of elements? Aug 12, 2022 · The documentation and the canonical examples of the ResizeObserver show that the callback function receives An array of ResizeObserverEntry objects that can be used to access the new dimensions of Apr 15, 2024 · ResizeObserver provides a more efficient and performant way to detect changes to the size of elements, and it also allows us to observe multiple elements at once. Makes child elements responsive to their parent container. Oct 27, 2021 · JavaScript has a native and easy-to-use API to listen for element resize. Jun 20, 2025 · ResizeObserver is only interested in layout geometry. This collection demonstrates how to use this API to create truly component-level responsiveness (Container Queries), where elements react to the size of their parent. I know it can be done using the ResizeObserver, but as its not supported in all browsers, i would Feb 24, 2020 · The ResizeObserver triggers but the window. log('Elements resized:', entries. Now that we know why we need the new ResizeObserver Api we will take a closer look at it. Jul 4, 2022 · Options (optional) ResizeObserver can observe different kinds of CSS sizes: content-box (default value): size of element's content area, border-box: size of element's box border area (content + padding + border), device-pixel-content-box: size of element's content area in device pixels. top}px ; ${cr. disconnect (); Practical Example Let’s put the Resize Observer API into practice with a simple Using multiple ResizeObserver instances can result in a noticeable performance penalty. observe(someElement); Angular 20. Jan 12, 2026 · The Intersection Observer API provides a way to asynchronously observe changes in the intersection of a target element with an ancestor element or with a top-level document's viewport. Together, these tools empower you to create responsive designs that adapt to the ever-changing landscape of modern web development. Apr 7, 2025 · Size changes caused by added elements: the Resize Observer API can help us react to size changes of an element that are triggered because of the dynamic addition or removal of elements. Gone are the days of inefficient polling or window resize listeners! Feb 8, 2023 · Start tracking the element's size with a call to ResizeObserver. observe(element), and . ResizeObserver lets developers observe size changes in elements and respond in real-time. Apr 23, 2023 · // entries is an array of ResizeObserverEntry objects // We only care about the first one, // since we call resizeObserver. As the name implies, a ResizeObserver observes whenever an element's dimensions change due to changes to the viewport size, the layout, or other factors. This approach is astoundingly more performant than using a ResizeObserver per element which most hook implementations do, Uses @juggle/resize-observer as a ponyfill when ResizeObserver isn't supported by the current browser, Dec 13, 2024 · This can be done using the unobserve() method: resizeObserver. observe(element). width}px x ${cr. contentRect; console. Nov 11, 2025 · This blog will guide you through integrating `ResizeObserver` into React 15 class components, covering **what elements to observe**, **where to place the observer logic** in the component lifecycle, and how to avoid common pitfalls like memory leaks. devicePixelRatio Oct 14, 2019 · The Resize Observer API allows you to detect when a particular element changes size and how large it is. The purpose of ResizeObserver is to expose a ResizeObserver DOM API that notifies observer when Element's size has changed. Install like May 19, 2024 · The ResizeObserver API in JavaScript offers an efficient way to monitor these changes. Check out the Example Playground for more information on usage and Apr 15, 2021 · It is safe to call observe multiple times on the same element as noted in the specs. [x] Automatically unobserves the target element when the hook unmounts. This is why ResizeObserver is a useful primitive. That’s where ResizeObserver comes in! With Nov 19, 2025 · Features [x] Uses a single ResizeObserver for tracking all elements used by the hooks. const resizeObserver = new ResizeObserver(callback); Polyfills the ResizeObserver API. ResizeObserver is a modern approach to handle element resize. at(0);. In this example, I only care about a single element but it's perfectly reasonable to watch multiple elements if you need to. var ro = new ResizeObserver( entries => { May 17, 2025 · Performance Tips: Always call unobserve() once the task is complete. Also, the callback passed to the ResizeObserver prints the new dimension of the div observed. Feb 11, 2020 · The ResizeObserver API is an interface for observing changes to Element’s size. This package provides you with: a context <Provider> with a ResizeObserver instance; a useResizeObserver() hook to observe any element's size changes. This instance will have an observe method that looks for changes to a specific element's size. log(`Element padding: ${cr. Stop fighting with window. May 21, 2019 · With the Resize Observer API, we can watch for resizing on individual elements! Dec 20, 2024 · The Resize Observer API is a browser feature that allows you to detect changes to the size of an element. Learn how to use it with this guide. This can be incredibly useful for creating responsive designs and optimizing the performance of your we Jul 25, 2018 · This seems to encourage having one ResizeObserver instance and observing and unobserving different elements as needed with logic in the callback to handle each entity. ResizeObserver Implements ResizeObserver spec, which has a nice explainer. resize event. Here’s another example, this time with multiple Jul 25, 2018 · The ResizeObserver has an observe() method and an unobserve() method. By the end, you’ll be able to track element resizes and update your component state reliably. unobserve(element). Explore this online useResizeObserver two elements sandbox and experiment with it yourself using our interactive online playground. If you would like to simply know when elements are visible, check out ngx-visibility. Zell discusses their API similarities, usage steps, refactoring strategies, and advantages with practical examples. Apr 22, 2021 · I have successfully matched the size using a resizeObserver but one part that falls down is if the page above the div I'm trying to cover changes height, the resizeObserver doesn't fire to move the covering div back into place - the x/y in resizeObserver callback is always 0/0. When the cake is done rising (the element is resized), the timer goes off (the callback is triggered)! Watching Multiple Elements Dec 13, 2024 · Understanding ResizeObserver The ResizeObserver API allows you to observe changes in the size of an HTML element. How Nov 26, 2024 · ResizeObserver returns an array of boxes for each element. For instance, you can use it to adjust the number of items in a row of a gallery or to change the layout of a card component based on its size. You can observer multiple elements but for our use case we only care about one, that's why I'm ignoring the other entries and just pulling out the first one - const entry = entries. This API improves performance and usability compared to traditional methods of monitoring size changes, which often relied on inefficient hacks or constant polling every few milliseconds, leading Jan 28, 2021 · Summary: Is there a way to get a list of the elements currently observed by a given ResizeObserver? Assume an existing ResizeObserver that observes some elements let observer = new ResizeObserver( A React hook that allows you to use a ResizeObserver to measure an element's size. length); May 6, 2023 · Each dynamically generated form input was like a new battlefield for ResizeObserver and LastPass, creating a loop of updates that pushed ResizeObserver to its limits. Here’s what you need to know. onresize doesn't. Initializing a ResizeObserver In order to initialize the Resize Observer, we use the ResizeObserver interface, passing it a callback function to run when the element being observed changes its dimensions. Callback function has one parameter of type array - entries. observe on a single element // If you're observing multiple elements, you'll have multiple entries in this array const entry = entries[0]; // log the new size of the element console. Learn more. You can observe multiple elements with one ResizeObserver. 😑 It's been in the editor's draft list for years. Why go through all this effort? Apps need to look Polyfills the ResizeObserver API. Jun 23, 2025 · The ResizeObserver constructor creates a new ResizeObserver object, which can be used to report changes to the content or border box of an Element or the bounding box of an SVGElement. This approach is astoundingly more performant than using a ResizeObserver per element which most hook implementations do. The only problem is it's not standard. Contribute to juggle/resize-observer development by creating an account on GitHub. It doesn't care if a new element is added or removed, unless that causes a size change. Why MutationObserver will tell you when the DOM element's child was removed, added or any of attributes of any DOM tree elements was changed. querySelector("h1")); Jul 31, 2023 · Imagine you’re a chef baking a cake. log(`Element size: ${cr. ResizeObserver’s notifications can be used to respond to changes in Element 's size. These changes trigger the observer API but don't trigger with the previous global resize event listener. Using a single instance of this ResizeObserver, I am observing on all the 20 divs. Mar 10, 2019 · I want to add a resize observer to a div element in my dom to give me a callback when it resizes. Aug 25, 2021 · This week I came across an extremely powerful API/hook called the “Resize Observer”. Understanding the ResizeObserver API The ResizeObserver JavaScript API allows developers to monitor changes in the size of an element on a webpage. Jun 23, 2025 · The ResizeObserver API provides a highly efficient and non-blocking way to observe size changes on any DOM element, not just the browser window. Sep 7, 2020 · It's called ResizeObserver and makes measuring dynamic elements very easy. Use a single observer for multiple elements when possible. This array just lists all the elements we are observing that have had their size change. Start using use-resize-observer in your project by running `npm i use-resize-observer`. observe(document. Apr 16, 2018 · The callback will be given an array of ResizeOberverEntries – one entry per observed element – which contain the new dimensions for the element. Return the cleanup function from useEffect that calls ResizeObserver. Oct 1, 2025 · Key Takeaways Resize events fire hundreds of times per second during window resizing, causing severe performance issues Throttling and debouncing are essential techniques to limit event handler execution frequency Modern alternatives like ResizeObserver API and CSS container queries often provide better performance Proper cleanup of event listeners prevents memory leaks in production applications Observe Elements: Use the observe() method of the ResizeObserver instance to start monitoring specific HTML elements. ⚛️ A React Hook to monitor changes in the size of an element using native ResizeObserver API 🔍 - Gautam-Arora24/resize-observer-hook May 14, 2024 · Are you ready? Let’s begin. It is an Element 's counterpart to window. May 9, 2024 · Understanding the ResizeObserver API The ResizeObserver JavaScript API allows developers to monitor changes in the size of an element on a webpage. idl implements a general observer pattern, observe (), unobserve Oct 3, 2024 · Question: What is this tutorial about? This tutorial shows how to use the ResizeObserver API in React and TypeScript to create responsive layouts. We can pass either one element or multiple: // resizeObserver. As the name implies, a ResizeObserver observes whenever an element’s dimensions change due to changes to the viewport size, the layout, or other factors. Jan 10, 2022 · Lazy loading, infinite scrolling, scroll based animations, and performant scroll events are all perfect examples of Intersection Observer in action. It immediately detects when an element resizes and provides accurate sizing information back to the handler. Easier to understand it as window. before (wrapper Oct 13, 2025 · ResizeObserver makes listening to element size changes precise, efficient, and elegant. The ResizeObserver constructor creates a new ResizeObserver object, which can be used to report changes to the content or border box of an Element or the bounding box of an SVGElement. You can use it as a template to jumpstart your development with this pre-built solution. observe(target, options); ro. Usage is simple, and pretty much the same as other observers, such as Performance Observer or Intersection Observer — you create a new ResizeObserver object using the ResizeObserver() constructor, then use ResizeObserver. Here, the ResizeObserver is like a kitchen timer alerting you to check the cake when it starts rising. Sep 21, 2021 · This will use the ponyfilled version of ResizeObserver, even if the browser supports ResizeObserver natively. The ResizeObserver interface reports changes to the dimensions of an Element's content or border box, or the bounding box of an SVGElement. Dec 22, 2020 · In this post we’ll see how we can use the new ResizeObserver API to react to an element’s size changing. Oct 1, 2023 · Resizing DOM Elements Effortlessly: A Practical Guide to ResizeObserver In the realm of modern web development, building responsive and adaptive user interfaces is paramount. Jan 30, 2018 · How many occasions have you attached a resize listener to a whole document just to track changes on a single DOM element? Those times are over — the Resize Observer is here. This allows you to know the size of each observed element. Jul 9, 2022 · Uses a single ResizeObserver for tracking all elements used by the hooks. x library to monitor changes to elements. - ZeeCoder/use-resize-observer Jun 17, 2024 · I was working on a problem where I have 20 divs (div-0, div-1, etc. ) and a ResizeObserver on the application level. Here’s what makes it great: It’s lightweight and easy to use May 28, 2022 · }); The key things to observer is that we create a new ResizeObserver with a callback that will be triggered whenever the element changes. So I have a ResizeObserver hooked up to watch for changes on my canvas Jun 7, 2020 · Link to the docs 2. log('Element:', entry. Build responsive components that actually work with JavaScript ResizeObserver. Architecture overview The externally exposed APIs are: ResizeObserver. Dec 2, 2024 · An example of using the ResizeObserver to correctly adjust the size of an HTML element containing dynamic content within a controlled layout. Apr 28, 2025 · Today, we’ll dive into the powerful ResizeObserver API — the modern and efficient way to detect when elements (not just windows!) resize. observe(), which adds our element as a new target to the list of observed elements. There are 350 other projects in the npm registry using use-resize-observer. Is there some way to observe the x/y position of a static element? Feb 20, 2022 · I am trying to get a self-resizing canvas following the recipe here (end of section 4, under "What to do instead"). Feb 16, 2023 · The ResizeObserver API is a relatively new feature in JavaScript that allows developers to detect changes in the size of an element on a web page. Sep 1, 2021 · What is ResizeObserver? The ResizeObserver API is a great tool for creating UIs that can adapt to the user’s screen and container width. This seems to encourage having one ResizeObserver instance and observing and unobserving different elements as needed with logic in the callback to handle each entity. 0, last published: 3 years ago. Jun 23, 2025 · Zell discusses refactoring the Resize, Mutation, and Intersection Observer APIs for easier usage, demonstrating how to implement callback and event listener patterns, while highlighting available options and methods. log(entry. Oct 20, 2024 · Container queries enable you to style elements based on the size of their parent container. contentBoxSize); Jul 26, 2024 · To use the Resize Observer API, you first need to create an instance of ResizeObserver and provide a callback function that will be called whenever the observed elements change size. Oct 23, 2019 · I'm observing multiple textareas with ResizeObserver. Jan 24, 2020 · A script creates a ResizeObserver with a callback which will be called with ‘observations’, and registers/unregisters callbacks using . If you want to be notified when DOM elements change properties, ngx-mutation-observer would be a good pick. Sep 22, 2024 · ResizeObserver takes one callback function, triggers any time an element you are observing changes size it will trigger the function passed to ResizeObserver. Dec 12, 2023 · For example, appending new children, setting an element's display style to none, or similar actions can change the size of an element, its siblings, or its ancestors. By observing elements, you can imperatively define your design breakpoints and change the element’s styles. function addNewItem () { function wrapIt (parentElem, selectors) { //Select the elements you want inside const divs_2 = parentElem. ResizeObserver provides a way to react to changes in element sizes, enabling you to create dynamic and responsive interfaces. Observing an element The last thing to do is to actually start observing an element. One of the benefits of ResizeObserver is making child elements responsive to their parent container. onresize doesn’t. MutationObserver What It will be helpful if you need to watch for DOM tree changes. May 2, 2025 · While the resize event fires only for the window nowadays, you can get resize notifications for other elements using the ResizeObserver API. Consider observing the parent container instead of the children if the children sizing affect the parent. Oct 15, 2024 · If you’re building responsive UIs with React, you’ve likely faced the challenge of handling element size changes in a smooth and efficient way. setAttribute ('id', 'third-column'); // add it to the DOM divs_2 [0]. Nov 1, 2024 · 1. This service can be used to create any tools that can benefit from using a single centralized ResizeObserver. Using a ResizeObserver, we can call a function whenever an element is resized, much like listening to a window resize event. A React hook that allows you to use a ResizeObserver to measure an element's size. target); console. Sep 28, 2019 · var ro = new ResizeObserver( entries => { for (let entry of entries) { const cr = entry. Set a threshold to balance sensitivity and performance. It works out-of-the-box, and can be a great addition to your toolset for building responsive design and dynamic UIs. React ResizeObserver Hook Observe multiple DOM elements with a single ResizeObserver. While it seems to do the job pretty well; it Feb 24, 2020 · The ResizeObserver triggers but the window. In short, the Resize Observer give you the ability to have entirely different elements rendered to the page The Resize Observer API is a powerful tool for tracking element size changes in web applications. Resize Observer works on individual elements. While currently this array always contains one item, it’s designed to support future multi-column layouts. Jun 16, 2025 · ResizeObserver, MutationObserver, and IntersectionObserver enhance performance over their predecessors. To do that we call ResizeObserver. Dec 13, 2024 · To utilize the Resize Observer API in your project, you need to first create an instance of the ResizeObserver, then define a callback function that will be called whenever size changes are detected, and finally connect it to the element you want to observe. Aug 5, 2024 · ResizeObserver can be seamlessly integrated with the CSS flexbox module to create responsive layouts that adapt to the available space. Some interesting facts about these observations: Observation will fire when watched Element is inserted/removed from DOM. Oct 23, 2019 · 7 How do I observe multiple elements with ResizeObserver like all textareas? Using document. Apr 11, 2023 · To use the ResizeObserver API you simply create a new ResizeObserver object instance using the constructor. height}px`); console. Feb 8, 2021 · Use a single instance of ResizeObserver and figure out at runtime what behavior should be used for a given element (which seems needlessly complex, and I don't know how reliable comparing element references would be in production), or Use multiple instances of ResizeObserver, which would make behavior simpler but theoretically reduce performance. Sep 4, 2025 · Ditch fragile CSS breakpoints. Nov 5, 2024 · ResizeObserver, on the other hand, gives us unlimited power to examine the entire DOM more precisely for multiple elements and write logic as complex as we want. Oct 14, 2016 · One thing that ResizeObserver allows you to do is to implement per-element media queries. left}px`); } }); // Observe one or multiple elements ro. 🚀 ResizeObserver in a nutshell Here is an example on how to use ResizeObserver to subscribe to a resize event of an element.

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Resizeobserver Multiple Elements. onresize to control the time after which the event fires. observe